Further characterization of the [Fe]‐hydrogenase from Desulfovibrio desulfuricans ATCC 7757

Abstract

The properties of the periplasmic hydrogenase from Desulfovibrio desulfuricans ATCC 7757, previously reported to be a single-subunit protein [Glick, B. R., Martin, W. G. and Martin, S. M. (1980) Can. J. Microbiol. 26, 1214–1223] were reinvestigated. The pure enzyme exhibited a molecular mass of 53.5 kDa as measured by analytical ultracentrifugation and was found to comprise two different subunits of 42.5 kDa and 11 kDa, with serine and alanine as N-terminal residues, respectively. The N-terminal amino acid sequences of its large and small subunits, determined up to 25 residues, were identical to those of the Desulfovibrio vulgaris Hildenborough [Fe]-hydrogenase. D. desulfuricans ATCC 7757 hydrogenase was free of nickel and contained 14.0 atoms of iron and 14.4 atoms of acidlabile sulfur/molecule and had ɛ₄₀₀, 52.5 mM⁻¹· cm⁻¹. The purified hydrogenase showed a specific activity of 62 kU/mg of protein in the H₂-uptake assay, and the H₂-uptake activity was higher than H₂-evolution activity. The enzyme isolated under aerobic conditions required incubation under reducing conditions to express its maximum activity both in the H₂-uptake and ²H₂/¹H₂ exchange reaction. The ratio of the activity of activated to as-isolated hydrogenase was approximately 3. EPR studies allowed the identification of two ferredoxin-type [4Fe-4S]¹⁺ clusters in hydrogenase samples reduced by hydrogen. In addition, an atypical cluster exhibiting a rhombic signal (g values 2.10, 2.038, 1.994) assigned to the H₂-activating site in other [Fe]-hydrogenases was detected in partially reduced samples. Molecular properties, EPR spectroscopy, catalytic activities with different substrates and sensitivity to hydrogenase inhibitors indicated that D. desulfuricans ATCC 7757 periplasmic hydrogenase is a [Fe]-hydrogenase, similar in most respects to the well characterized [Fe]-hydrogenase from D. vulgaris Hildenborough.